In order to investigate the water conservation effects of Eucalyptus urophylla×E. grandis and Acacia crassicarpa plantations,plots with similar stand conditions were selected, and comparative studies were made on water-holding capacity of canopy, vegetation layer under canopy, litter layer and soil. Results showed that water-holding capacity in different layers of two different plantations were in the order of soil layer＞litter layer＞canopy＞vegetation layer under canopy. The water-holding capacity of canopy, litter layer, and the water-holding capacity of soil were in the order of A. crasscarpa plantation E.urophylla×E.grandis plantations, but the water-holding capacity of layer under canopy was just the opposite. The total water-storage capacity both above ground and soil in E.urophylla×E.grandis and A. crasscarpa plantation were 1 852.82 and 1 917.72 t/hm² respectively， and the total value of water conservation for the two plantations were 1 241.39 and 1 284.87 yuan/hm², respectively.